Electronic power converters accept electric power from an input source and convert it into a form suitable for use by a load. As defined herein, power converters are devices that convert electric power from an AC source or a DC source to deliver it to a load at an AC voltage or a DC voltage while providing some of the following functions: voltage step-up, voltage step-down voltage regulation, with or without galvanic isolation. Examples of power converters include DC-DC converters, switching regulators and active filters.
The power density of a power converter as defined herein is the full rated output power of the power converter divided by the volume occupied by the converter. Trends in contemporary power conversion have resulted in dramatic increases in power density of marketable power converters. Prior to 1984, power densities were typically below 10 Watts-per-cubic-inch. In contrast, power densities greater than 500 Watts-per-cubic-inch have become possible today. A very high density, galvanically isolated, point of load DC-to-DC transformer, called a “VTM” is described by Vinciarelli in U.S. patent application Ser. No. 10/066,418, filed on Jan. 31, 2002, entitled “Factorized Power Architecture With Point of Load Sine Amplitude Converters,” and in the CIP application Ser. No. 10/264,327, filed Oct. 1, 2002 (the “Factorized Application”).
The current density of a power converter is defined herein as its full rated output current divided by the board area occupied by the converter. Escalating current requirements of microprocessors (CPU's), now approaching 100 Amperes, and the need to provide such currents within a small footprint in close proximity to the CPU has gone beyond the capacity of contemporary power supply technology. Commercially available solutions are characterized by a current density of less than 10 A/in2 and are inadequate to support future CPU requirements. Sine Amplitude Converters, of the kind described in the Factorized Application ibid, are capable of providing the low voltage requirements of future microprocessors with current densities exceeding 50 A/in2. They utilize a two-sided circuit board assembly including transformer core structures protruding from both sides of the circuit board. Output currents in excess of 50 Amperes need to be carried from the converter's PC board, at one elevation, to the CPU board, at a different elevation. These interconnections need to be made with low resistance and inductance, consistent with the current slew rate requirements of a highly dynamic load.
Power converters dissipate heat in operation. Increases in power density make thermal management more difficult, particularly where the increase in power density exceeds the corresponding increase in efficiency causing a net increase in heat density. Thus, advancements in power conversion technology may often present significant challenges in terms of thermal management technology. These challenges impose constraints on the packaging architecture used to house the converter and its input and output terminals: the package must exhibit low thermal resistance between its internal hot spots, particularly its semiconductor junctions, and external heat sinks. Depending on the specific thermal environment surrounding the power converter, it is desirable to remove heat from the converter package through its case and/or terminals. Low junction-to-case and junction-to-terminal thermal resistances are required to keep internal temperature rises acceptable. And the need for a good thermal interface must not interfere with the need for flexible mounting of the power converter package, while respecting constraints associated with mechanical tolerances of the converter package and of the system with which the converter is coupled.
One way to mount a high-density power converter, shown in FIG. 1, is described in Vinciarelli et al, U.S. Pat. No. 5,526,234, “Packaging Electrical Components” (assigned to the same assignee as this application and incorporated by reference). In the Figure, steps on the case of a power converter 10 allow the upper wall of the converter 12 to lie within a hole 14 in circuit board 16. The effective height of the combined power converter package and circuit board is reduced because a portion of the height of the package is coextensive with the thickness of the circuit board 16. Thermal management is enhanced because both the upper and lower surfaces 12, 13 of the power converter are exposed for heat removal (e.g., by use of forced air or by heat sink attachment). The power density of power converter 10, on a stand-alone basis, is the full rated output power of the converter divided by the total volume occupied by the converter. However, the equivalent power density of the converter, when mounted as shown in FIG. 1, is higher than the stand-alone power density because a portion of the height of the power converter package is coextensive with the thickness of the circuit board 16 and the incremental volume occupied by the converter above and below the circuit board 16 is less than the total volume of the stand-alone converter.
SynQor, Inc., Hudson, Mass., USA manufactures DC-DC power converters and DC transformers which comprise components mounted on both sides of a printed circuit board and magnetic components which pass through apertures in the printed circuit board and pins for connection to another circuit board. One such converter, called a “BusQor™ Bus Converter,” is described in data sheet “Preliminary Tech Spec, Narrow Input, Isolated DC/DC Bus Converter,” SynQor Document No. 005-2BQ512J, Rev. 7, August 2002.
Vinciarelli et al, U.S. Pat. No. 6,031,726, “Low Profile Mounting of Power Converters with the Converter Body in an Aperture” (assigned to the same assignee as this application and incorporated by reference) describes power conversion apparatus in which a power converter 20 extends through an aperture 21 in a circuit board 23. One such embodiment is shown in FIGS. 2A through 2C. In the figures, the power converter 20 is mechanically and electrically connected to a terminal board 22 and power and signal inputs and outputs are routed, via conductive runs and solder connections, from contact pads 26 on the terminal board to contact pads 24 which extend from the power converter body. A heat sink 27 surrounds the outside of the power converter to aid in heat removal. The length, L2, of the terminal board 22, is greater than the length, L1, of the aperture 21 in the circuit board 23. The contact pads 26 are connected by solder (not shown) to runs 25 on the circuit board 23. Because a portion of the body of the power converter 20 is coextensive with the circuit board 23, the equivalent power density of the power converter is greater than the stand-alone power density, as explained above with respect to FIG. 1.
A power conversion apparatus, in which a power converter is mounted in an aperture in a circuit board, and in which a compliant connection scheme along the sides of the power converter allows for variation of the extension of the power converter within the aperture, is described in Vinciarelli et al, U.S. patent application Ser. No. 09/340,707, filed on Jun. 29, 1999, and entitled “Mounting Electronic Components on Circuit Boards.” A power conversion apparatus, in which a power converter is mounted in an aperture in a circuit board, and in which at least four sides of the power converter, including the two sides which lie entirely above and below the surfaces of the circuit board, are covered with heat sinks to aid in the removal of heat from the power converter, is described in Vinciarelli et al, U.S. Pat. No. 6,434,005, “Power Converter Packaging” (assigned to the same assignee as this application and incorporated by reference).
Takatani, Japan Patent 2-142173, “Integrated Circuit Part and Mounting Structure Thereof” describes an assembly 450, shown in FIG. 18, consisting of a pair of over molded integrated passive networks 452, 453 connected by leads 454 to circuit etches (not shown) on both sides of a substrate 456. As shown in the Figure, the assembly may be mounted over an aperture 458 in a printed circuit board 460 so that the over molded integrated passive network 453 on one side of the substrate pass into the aperture and contact pads 460 arranged on the surface of the periphery of the substrate 456 are soldered to mating contacts 462 on printed circuit board along the periphery of the aperture 458.
Techniques for over molding electronic components on one side of a substrate are known. In one example, electronic devices mounted on one side of a printed circuit board assembly are over-molded with encapsulant and the other side of the printed circuit board assembly, which is not over-molded, comprises a ball grid or a land grid array of electrical contacts. FIG. 13 illustrates a ball grid array package of the kind shown in a datasheet for a “Full Function Synchronous Buck Power Block”, model iP1001, published by International Rectifier, El Segundo, Calif., USA. In the figure, power conversion circuitry (not shown) consists of components mounted on top of a circuit board. The components and the board are over-molded with encapsulant to form a packaged device 232. A ball grid array of contacts (e.g., contacts 233 in FIG. 13) is arranged along the bottom surface of the device. In application, the ball grid array of contacts is soldered to mating contact pads or runs (e.g., contact pads 235) on the surface of a printed circuit board (“PCB”) 239. The package architecture exemplified above, sometimes referred to as “System In a Package” (SIP), provides some of the electrical, mechanical and thermal management characteristics required of high power density and high current density converters. However, the SIP architecture is incompatible with two-sided circuit board assembly including transformer core structures protruding from both sides of the circuit board, as described in the Factorized Application ibid. Furthermore, the SIP package provides limited mechanical and thermal management flexibility.
Intel Corporation, Santa Clara, Calif., USA, manufactures microprocessors which are packaged in a package, called a Micro-FCPGA package, which comprises a component over molded on one side of a substrate and a pin-grid-array and exposed capacitors on the other side of a substrate.
Saxelby, Jr., et al, U.S. Pat. No. 5,728,600, “Circuit Encapsulation Process” and Saxelby, Jr., et al, U.S. Pat. No. 6,403,009, “Circuit Encapsulation” (both assigned to the same assignee as this application and both incorporated in their entirety by reference) describe ways of over-molding both sides of a printed circuit board assembly while leaving opposing regions on both sides of the printed circuit board free of encapsulant. This is useful for exposing a row of contacts that extend along an edge of the printed circuit board on both sides of the board.